Breech loadable shotgun cartridges are well known, typically comprising either a fibre or plastic wad. Fibre wads are usually disc-shaped, configured to provide a gas-tight barrier between a powder charge at one end of the cartridge and a plurality of shot, or a single slug, within a cardboard or plastic cartridge sleeve which is capped at one end by a brass cap. Plastic wads generally comprise a charge barrier connected by a compression zone to a receptacle for holding shot. The compression zone is compressed in the cartridge to aid in compacting the powder charge. The compression zone may also compensate for different hull lengths and shot loads, or may be reduced or removed for steel and heavy loads because of larger shot volumes required.
The brass cap has a primer therethrough for igniting the charge. The cartridge is sealed at the other end by using a known “roll-turn-over” (RTO) method of crimping the end of the sleeve over the opening. A cardboard or fibre disc is inserted in the sleeve on top of the shot or slug prior to the RTO of the sleeve, for the turned in sleeve edge to bear against. Another known method of sealing the other end of the of the cartridge is “crimping”, which is achieved by inserting the disc in the sleeve on top of the shot, or wad, and crimping inwardly the end of the sleeve to retain the disc.
In use, the cartridge is placed into the breech of a shotgun barrel and the primer struck to ignite the charge. A rapid expansion of gas from the ignited charge then forces the shot carrying wad from the barrel's muzzle. When the wad leaves the muzzle, it is abruptly slowed down due to friction with surrounding air, and the shot travels forward from the wad toward its target.
Shot has traditionally been made from lead, which is relatively soft compared to a shotgun barrel and therefore does not damage the barrel when fired. Due to increasing awareness of the detrimental effects of spent lead shot on flora and fauna, there has been a concerted effort in recent years to replace lead shot with shot made from other materials. Some authorities have also banned the use of lead shot in certain areas. Examples of lead shot replacement materials include steel, bismuth, tungsten-iron, tungsten-nickel-iron and tungsten-polymer. Steel is a preferred replacement to lead for reasons such as low environmental impact and relatively low cost. However when used with fibre wads, steel shot tends to damage shotgun barrels. Steel shot therefore necessitates the use of plastic wads, since the shot receptacle protects the barrel from contact with the shot during its passage through the barrel. The design of the plastic wad has the added advantage of improving the shot grouping or firing pattern due to radially constraining the shot prior to leaving the barrel.
However, as wads are typically left where they fall when fired from a gun, there is increasing concern as to potential detrimental environmental and aesthetic effects of plastic wads littering the areas in which shotguns are used.
It is an object of at least a preferred embodiment of the present invention to overcome or ameliorate at least one of the deficiencies of the prior art, or at least to provide a suitable alternative thereto.